Automatic precision liquid loading control method

ABSTRACT

A fixed fluid control system for loading fluids into sealed tanks includes pressure sensing conduits in a mobile vehicle and fixed fluid controls. In the vehicle are first and second pressure sensing conduits having portions within the sealed tank positioned at the top and bottom of the tank. The pressure sensing conduits have exterior portions to which are detachably coupled additional pressure sense lines. The additional pressure sensing conduits are coupled to a differential pressure to current converter within the fixed fluid control system. The converter produces a current signal proportional to the pressure difference between the two sense lines. When this current reaches a predetermined high level, the supply of fluid to the sealed tank is discontinued.

This is a division of application Ser. No. 690,233, filed Jan. 10, 1985,now U.S. Pat. No. 4,649,968.

BACKGROUND OF THE INVENTION

A. Field of the Invention

This invention relates to the field of loading fluid into trailers andin particular to control of such loading from a fixed control system.

B. Background Art

When loading volatile liquids, such as cryogenic liquids, into sealedtanks inside trailers, it is difficult to assure safety and accuracy.Conventionally, a differential pressure meter is provided at the rear ofthe trailer. This meter was used to obtain an indication of the level ofthe liquid within the tank. However, trailer-mounted analog liquidgauges are inherently inaccurate, having an accuracy of only plus orminus one percent when new. Furthermore, because this differentialpressure meter is permanently attached to the trailer, it is subject toa great deal of vibration and other abuse which causes the accuracy todeteriorate to plus or minus five percent or worse after a period ofuse.

With respect to safety, it was required that the person filling thetrailer be present where the differential pressure meter is mounted atthe rear of the trailer in order to observe the meter. This location isin proximity to the coupling between the flexible filling hose and theintake connection. Thus, any accidental spilling of the liquid, blow-offof excess pressure, or other type of accident exposed this person todanger, particularly if the fluid or its vapors were toxic. In order tocontrol filling manual opening and closing of a valve in the supply pipehas been required. This resulted in inaccuracy because manual closing ofthe valves could take as long as three to five minutes.

The vibration due to driving and road dust and dirt causes linkageswithin the differential pressure gauge to stick. Additionally, theenvironment within the rear of the truck where the differential pressuregauge is mounted is very severe. If the liquid stored in the tank is acryogenic liquid, the rear is cold and foggy. These conditions combineto cause the accuracy of truck-mounted differential pressure gauges todecline to ±5% or worse.

A more accurate method of controlling level has been in the use of adirect acting weight scale. However, it does not eliminate the danger tothe operator and it is very costly to retrofit a facility with scales.

U.S. Pat. No. 4,266,580 shows a system for loading tank cars. U.S. Pat.No. 3,618,643 (Hovant) teaches a loading bay for filling thecompartments of a vehicle with liquid fuel. However, neither of thesepatents are considered suitable or readily adaptable for use in loadingcryogenic liquids into sealed tanks because they include inserting anapparatus into the tanks being loaded.

For purposes of considering the patentability of the invention disclosedand claimed herein, a brief patentability search has been conducted. Inaddition to the patents mentioned above, other patents identified to beof possible interest in this search were:

    ______________________________________                                               3,494,387    Gillies et al                                                    3,916,961    Dilger                                                           3,983,913    Bower                                                            4,082,122    McGahey                                                   ______________________________________                                    

However, none of the devices taught by the foregoing patents appearsadaptable to automatic precision liquid loading of cryogenic liquids.

It is an object of the present invention to provide a system for fillingsealed tanks with fluid wherrein the level of fluid may be controlledwith precision.

It is an additional object of the present invention to provide a systemfor filling sealed tanks in trailers in which operator control functionsare performed remotely from the trailer to assure operator safety.

SUMMARY OF THE INVENTION

A fixed fluid control system for loading fluids into sealed tanksincludes pressure sensing conduits in a mobile vehicle and fixed fluidcontrols. In the vehicle are first and second pressure sensing conduitshaving portions within the sealed tank positioned at the top and bottomof the tank. The pressure sensing conduits have exterior portions towhich are detachably coupled additional pressure sense lines. Theadditional pressure sensing conduits are coupled to a differentialpressure to current converter within the fixed fluid control system. Theconverter produces a current signal proportional to the pressuredifference between the two sense lines. When this current reaches apredetermined high level, the supply of fluid to the sealed tank isdiscontinued.

BRIEF DESCRIPTION OF THE INVENTION

FIG. 1 shows in block and diagrammatic form the automatic precisionliquid loading control system of the present invention.

FIG. 2 is an expanded view of a portion of the permanent pressureconduits id FIG. 1.

FIG. 3 shows a block diagram of the fixed portions of the system of FIG.1.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows the automatic precision liquid loading control system 10including mobile vehicle 12, and a fixed station 10a comprising acontroller 58, liquid duct 34, valve 38 and supply hose 42. Vehicle 12is a conventional truck or trailer and includes a sealed tank 56 and arear compartment 60. While sealed tank 56 may be used to transport anyliquid, it preferably contains a cryogenic liquid. Within sealed tank 56are pressure sense conduits or lines 16 and 18. Pressure conduit 16 ispositioned near the top of tank 56 to detect the pressure of the vaporspace above the liquid which may be stored in tank 56. Pressure senseconduit 18 is positioned near the bottom of tank 56 in order to sensethe pressure at the bottom of tank 56. The pressure at the bottom oftank 56 is the sum of the vapor space pressure sensed by conduit 16 andthe pressure caused by the level of liquid stored in tank 56. Thus, thedifference between the pressure sensed by conduits 16 and 18 is relatedto the level of liquid within tank 56.

Within rear compartment 60, conventional differential pressure meter 19determines the difference between these two pressures. Differentialpressure meter 19 is coupled between pressure sense conduits 16 and 18and produces a reading proportional to the difference between thepressures in conduits 16 and 18, which is proportional to the height ofliquid within tank 56. A thermal valve 21 is provided on pipe 16 torelease excessive pressure as a safety measure. To provide insulation,tank 56 has two layers, and the space between the layers is evacuated.

Also within compartment 60 are connectors 20, 22 which are fixedlycoupled to pressure sensing lines 16, 18 respectively. Connectors 20, 22are detachably coupled to pressure sense lines 24 and 26 respectively,thereby allowing pressure sense lines 24, 26 to be detachably coupled topressure sense conduits 16, 18. Thus, the pressure in line 24 issubstantially equal to the pressure sensed by conduit 16 within tank 56and the pressure within line 26 is substantially equal to the pressuresensed by conduit 18 within tank 56.

Lines 24, 26 are also coupled to fixed controller 58, thereby applyingto controller 58 the pressures sensed by conduits 16, 18. If trailer 12contains a volatile or toxic substance which must be kept at a safedistance from controller 58, lines 24, 26 may contain a diaphragm and anincompressible fluid to couple the pressure of tank 56 to controller 58.

Liquid duct 34 is an insulated enclosure which carries liquid to thesite where truck 12 is loaded. Liquid is carried from liquid duct 34through liquid supply pipe 36 and flexible supply hose 42. Supply pipe36 is provided with a thermal valve 23 for safety. In conventionalmanner, supply hose 42 is coupled to truck 12 in order to supply liquidfrom liquid duct 34 to tank 56 within truck 12. Liquid supply pipe 36includes a pneumatically controlled valve 38.

Within controller 58, pressure sense lines 24, 26 are coupled todifferential pressure monitor 28. Differential pressure monitor 28produces a signal proportional to the difference between the pressure inpressure sense lines 24, 26. This difference is related to thedifference between the pressure at the top and bottom of tank 56 and is,therefore, proportional to the level of liquid within tank 56.

When the differential pressure reaches a predetermined set point, apneumatic signal is applied through a pneumatic line 79 which controlsvalve 38 to close pipe 36. Thus, a predetermined precise level of liquidwithin tank 56 may be obtained without operator intervention. Controller58 includes a three position selector switch 41 which permits selectionof the foregoing automatic mode of filling or manual filling, orshutdown of controller 58. When manual filling is selected valve 38 isopened and none of the functions of controller 58 are performed.

In FIG. 2, pressure conduit 16 is shown having a section 16a within tank56 and a section 16b exterior to tank 56. Because sealed tank 56 mustwithstand the vapor pressure caused by storing a cryogenic liquid, welds60, completely surrounding sense pipe 16, are performed to completelyand permanently seal the hole in each layer of tank 56 through whichpipe 16 passes. Similarly, welds 61 completely seal the hole in eachlayer of tank 56 through which pipe 18 passes at the junction ofinterior portion 18a and exterior portion 18b.

The exterior sections 16b, 18b are at the same pressure as interiorsections 16a, 18a, respectively. The exterior sections 16b, 18b arecoupled to differential pressure gauge 20.

Conduits 16b and 18b are coupled to connectors 20, 22, respectively.Connectors 20, 22 are conventional connectors, each having two connectorportions which may be coupled to each other. Connector portion 20a issecured to line 24 and portion 20b is secured to conduit 16b. Similarly,connector 22 has portions 22a,b secured to lines 26, 18b, respectively.

In conventional manner, coupling is accomplished by sliding back aspring loaded sleeve on section 20b or 22b, inserting section 20a or22a, and releasing the sleeve. Alternatively, one of the sections 20a,22a may be secured to a conduit 16, 18 and the corresponding section20b, 22b may be secured to a line 24, 26. If one of the connectors 20,22 is reversed in this manner, it is impossible to couple lines 24, 26to the incorrect conduits 16, 18.

In FIG. 3, pressure sense lines 24, 26 are coupled to differentialpressure to current converter 60 of monitor 28. Monitor 28 alsocomprises a display 62 and a comparator 64. In conventional manner,converter 60 converts the difference betwen the pressures of pressuresense lines 24, 26 into a current signal. The magnitude of the outputcurrent signal from converter 60 may vary, for example, from 4-20milliamps as the differential pressure varies from zero to maximuminches of water or pressure.

The output current signal of converter 60 is applied to display 62.Display 62, preferably LED, displays a pressure reading between zero andthe maximum inches of pressure depending on the magnitude of the currentsignal applied by converter 60. Additionally, display 62 applies thecurrent signal from converter 60, without alteration, to comparator 64.

Comparator 64 compares the current signal with two predetermined setpoints. One set point is selected to represent a ninety percent fullcondition for a tank 56 of trailer 12 being filled. The secondpredetermined set point is selected to represent a one hundred percentfull level. Thumbwheel switch set point selectors 66, 68, as shown inFIG. 1, are coupled to comparator 64 and permit the manual selection ofthese two set points as appropriate for a particular trailer 12 beforefilling begins.

When comparator 64 determines that the current signal produced bydifferential pressure to current converter 60 is substantially equal tothe selected level representative of tank 56 being ninety percent full,comparator 64 applies a DC signal to a solid state photo-isolator relay74. This causes photo-isolator 74 to supply energy from supply line 86to relay 82. When relay 82 is energized, a delay 84 is initiated and analarm 46 is activated. When a predetermined period of delay time haspassed, delay 84 deactivates alarm 46. Thus a temporary warning alarm isprovided when trailer 12 reaches the ninety percent level.

Photo-isolator relay 74 is effective to isolate the sensitive circuitryof comparator 64 from the large transients which occur when current isswitched to relay 82 from supply line 86. Additionally, other relays,such as relay 80, are isolated from these transients when relay 82 isenergized thereby preventing the energizing of relay 82 from causingother relays to be improperly energized.

When comparator 64 determines that the signal produced by converter 60is representative of the one hundred percent full level of trailer 12,comparator 64 applies signals to photo-isolated relays 70, 72. Whencomparator 64 applies the one hundred percent full signal tophoto-isolator 72, it causes energy from supply line 86 to be applied torelay 80, thus actuating relay 80 which activates alarm 46. Thus, analarm signal is provided to warn the operator that trailer 12 is onehundred percent full and alarm 46 must be manually deactivated.

Photo-isolated relay 70 supplies energy from energy source 86 topneumatic control 78 during filling of tank 56, thereby causing normallyclosed valve 38 to remain open. However, when photo-isolator 70 receivesthe one hundred percent full signal from comparator 64, it causes energyfrom supply 86 to be disconnected from pneumatic control 78. Whenpneumatic control 78 is thus deactivated, it prevents air from passingfrom an air supply 77 to pneumatic control air line 79, thus causingnormally closed valve 38 to close. As shown in FIG. 1, when valve 38 isclosed, liquid from supply pipe 36 is prevented from passing throughfilling hose 42 into tank 56. Thus, when comparator 64 determines thattank 56 is one hundred percent full, comparator 64 causes the filling oftank 56 to stop by closing valve 38 and warns the operator by activatingalarm 46.

All of the energy supplied from supply 86 to photo-isolated relays 70,72, 74 must pass through high pressure auto-valve shutdown switch 30 andselector switch 41. Switch 30 is coupled to pressure sense line 24 byline 48. When shutdown switch 30 determines that the pressure in line 48has risen above a predetermined threshold, all power to circuits 60, 62,64, 70, 72, 74 is shut down, closing normally closed valve 38. Pressureswitch 30 thus provides emergency backup protection for any overfillwhich may occur. One way in which such a condition may be caused is byimproper set point selection.

If sector switch 41 is in the AUTO position, power is supplied to theelements of controller 58. However, if switch 41 is in the MANUALposition indicating manual operation, power is supplied from PSH 30 onlyto pneumatic control 78 to constantly actuate valve 38 to the openposition. To close valve 38, switch 41 is turned to the OFF position.

Thus, fixed system 10a permits a mobile vehicle to be filled by backinga vehicle 12 up to system 10a, coupling pressure sense lines to conduitsin the vehicle and coupling a filling hose to the vehicle. The operatorthen indicates set points and places the selector switch 41 into theAUTO position, thereby initiating filling. When system 10 determinesthat the vehicle is full and stops the flow of the liquid, the operatordisconnects the sense lines and the filling hose and the vehicle may bedriven away.

It is anticipated that the aspects of the present invention, other thanthose specifically described and illustrated will be apparent from theforegoing description and the drawings, and many other variants of theinvention may be devised.

For example, a heater may be included within the housing of controller58 to assure reliable operation at low temperatures. This heater may bea conventional thermostatically controlled electrical heating elementwith a fan to force air across the heating element. For adequatetemperature control, the exposed inner surface of the housing ofcontroller 58 may be covered with an insulating material such asstyrofoam.

The appended claims are intended to be construed to encompass all suchvariants and aspects which are within the true spirit and scope of theinvention.

In automatic precision loading system 10, the following components havebeen used for the operation and function as described and shown:

    ______________________________________                                        Reference                                                                     Numeral      Type                                                             ______________________________________                                        20, 22       Swagelok QF4, Solon, OH                                          30           4NN-K45-ClA-Sl-BB-TT-X,                                                       Static O-Ring, Olise, KS                                         60           1151 DP-4E-2AB-2-T02B7, Rosemont,                                             Minneapolis, MN                                                  62           400A13, Doric, San Diego, CA                                     64           411A-003A, Doric, San Diego, CA                                  70, 72, 74   W-6110DTX-1, Magnacraft                                          78           8302A81F, Asco                                                   ______________________________________                                    

What is claimed is:
 1. A method of loading fluid from a sourcecontrolled by a fixed station having differential pressure sensing meansinto a sealed tank of a mobile vehicle having first and second pressuresensing conduit means each sensing unequal substantially high pressuresin the tank comprising the steps of:(a) supplying fluid into the sealedtank through a supply conduit separate from the first and secondpressure sensing conduit means; (b) detachably coupling first pressuretransmitting conduit means to the first pressure sensing conduit means;(c) applying a first pressure to the differential pressure sensing meansby way of the first pressure transmitting conduit means for sensing thepressure within the first pressure sensing conduit means; (d) detachablycoupling second pressure transmitting conduit means to the secondpressure sensing conduit means; (e) applying a second pressure unequalto the first applied pressure to the differential pressure sensing meansby way of the second pressure transmitting conduit means for sensing thepressure within the second pressure sensing conduit means; (f) sensingthe substantially small value differential pressure between the firstand second pressure sensing conduit means by the differential pressuresensing means wherein the sensed differential pressure value issubstantially small relative to the pressures of the first and secondpressure sensing conduit means and producing a differential pressuresignal related to the substantially small value differential pressurewithin the tank; (g) producing a differential pressure set point signalwhen the produced differential pressure signal is beyond a predeterminedset point; and (h) controlling the supply of fluid free of measurementwithin the supply conduit in response to the differential pressure setpoint signal.
 2. The method of claim 1 in which the first and secondpressure sensing conduit means respectively sense a first pressure of avapor space above the fluid and a second pressure substantially near thebottom of the tank.
 3. The method of claim 1 in which the sensing ofdifferential pressure comprises converting from differential pressure toan electrical differential pressure signal and transmitting theelectrical differential pressure signal as the produced differentialpressure signal.
 4. The method of claim 2 further comprising the step ofdetermining when the pressure of a vapor space above the fluid in thetank is above a predetermined pressure set point signal and controllingthe supply of fluid in response to the vapor space pressuredetermination.